It threatens to be so true to life that it's more like a documentary than a feature film. "I'm surrounded by cretins!" shouts a stack-heeled, would-be French president at his terrified advisers. "Remember, I'm a Ferrari. When you open the bonnet, you use white gloves."

When the Cannes film festival opens next week, it will break the last taboo in French film. La Conquête, a scathing portrait of Nicolas Sarkozy's rise to power - the first French feature film brave enough to tackle a serving president - will be shown on La Croisette after a row over whether officials wanted to sideline it to spare the Elysée's blushes.

Inspired by the merciless British satire In the Loop, and subtitled "The man who won the presidency, but lost a wife", it hopes to skewer Sarkozy's rage, ambition and problems with women. But it faces the same problem as Italian director Nanni Moretti's Berlusconi-inspired The Caiman: how do you parody a man who has already become a parody of himself?

This year's Cannes is already displaying an unprecedented Sarkozy theme. The first lady, Carla Bruni, will appear in Woody Allen's Midnight in Paris, while the French director Pierre Schoeller's L'Exercice de l'Etat fictionalises the personal sacrifices of a government minister.

Sarkozy, record-breakingly unpopular one year before a tough battle for re-election, cannot risk appearing on the red carpet himself, nor can Bruni. It would send the wrong message about lavish partying to cash-strapped France.

But the Elysée is already on a damage-limitation offensive over La Conquête. In recent days, Sarkozy has been brandishing a three-page handwritten letter from the actor who plays him. Denis Podalydès is one of France's biggest theatre stars, a leftwinger whose line in Shakespearean figures like Richard II has set him up well for playing right-winger Sarkozy's 2007 rise to power. He recently wrote to Sarkozy explaining his role in the film, which the president has taken as an admission that the film isn't too cruel.

But the Elysée is clearly irked by the film. Several Sarkozy advisers have dismissed the trailer as "a ridiculous caricature". Producers said French TV channels self-censored and refused to contribute funding for the "dangerous and risky project" and the script was leaked, perhaps reaching as high as the Elysée. Rachida Dati, the former Sarkozy protégée and minister, reportedly tried to contact the actor playing her, but was brushed off.

This week Carla Bruni admitted she was "worried" about the film, which depicts Sarkozy's split from his previous wife, Cécilia. She said: "It's a period that I experienced like everyone else, observing the presidential candidates from the outside. I would really like to watch this film with that same sense of distance, but I'm not sure I can."

Even the film poster has made the political class cringe. Designed by the English team who worked on In the Loop, it shows a pair of short legs in stacked heels, dangling off a high stool, echoing a scene in the film where the diminutive Sarkozy throws a tantrum that his chair is too high.

Podalydès has described his Sarkozy character as both "endearing and insufferable", "mature and immature", someone totally "animal" who cares little about philosophy. He recently met Sarkozy at the Elysée and said the president told him: "I don't like power, but I like exercising it."

The script is based on an analysis of Sarkozy by the political historian and documentary maker, Patrick Rotman. But French critics have warned they want more than just accurate Sarkozy-mimicry and hunger for a piece of fiction that explores the president's narcissistic yet unfathomable personality.

Le Figaro's Sebastien Le Fol said he wanted the emotional resonance of British films like The Queen or the Tony Blair-Gordon Brown drama, The Deal. "La Conquête will only win us over if it allows us to enter the unconscious of a man of state and reveal the workings of power."

Other key Cannes films

The Tree of Life The reclusive American film-maker Terrence Malick's family drama with mysterious cosmic element. It's only his fifth feature in 40 years.

Melancholia A sci-fi, apocalyptic wedding drama, from the Danish maverick director Lars Von Trier who shocked Cannes with the film Antichrist in 2009.

This Must Be The Place Sean Penn plays a 50-year-old ex-rocker who travels across the US on the trail of a Nazi war criminal.

The Skin I Live In Spanish director Pedro Almodovar's creepy revenge saga about a plastic surgeon.

Death of a Samurai Japanese director Takashi Miike's honour and revenge story is billed as the first 3D film to be shown at Cannes.

We Need To Talk About Kevin Lynne Ramsay's family drama based on the novel about middle-class parents struggling to make sense of a high-school massacre is Britain's competition hope.

• This article was amended on 9 May 2011. The original referred to "a ridiculous charicature". This has been corrected.